forgot to update the animation hooks accordingly; x is the filename now, but I need basename and extension here
closes #597 again: now we use options(knitr.chunk.foo) and options(knitr.package.foo)

backward compatibility is preserved for now
a hack to allow myself to modify opts_chunk locally

I set R_KNITR_OPTIONS="knitr.chunk.tidy=TRUE" in ~/.Renviron
typo
cosmetic
tweak other affected plot hooks (x is filename instead of c(basename, ext) now)
fixes #663: shortcode in knit2wp() can be a vector of length 2